The commercialization of the DSC (Differential Scanning Calorimetry) technique in the 1960s led to a rapid expansion of this method for the thermal characterization of materials. The great strength of DSC is that complex information can be quickly and easily obtained about physical transitions, the structure of materials as well as the kinetics and composition of chemical reactions.
Conventional DSC instruments allow measurements to be performed at heating rates of up to 500 K/min and cooling rates of 200 K/min with a signal time constant of about 1 to 2 seconds. This is not adequate for the investigation of the structure and morphology of polymers and polymorphic substances or of meta-stable materials in general. Semi-crystalline polymers are meta-stable; their structure, thermal and mechanical properties depend on their thermal history. Different cooling rates can lead to changes in the meta-stable structure when they are cooled from the melt. This specific reorganization often cannot be measured in the DSC because the result curve consists of exothermic and endothermic events that take place simultaneously. A new technology is needed to further investigate these systems and simulate high speed production processes such as injection molding that use cooling rates of up to several hundred Kelvin per second.
The Flash DSC 1 (Fig. 1) is a completely new type of commercial DSC with a signal time constant of less than 1 millisecond. This allows very high heating and cooling rates to be achieved in the range is 1 K/s to 40,000 K/s (60 K/min to 2,400,000 K/min). The heating rate overlap with conventional DSC is complimentary and offers over six decades of heating rate for experimentation. The UFS 1 MultiSTAR sensor is based on MEMS technology (MEMS: Micro-Electro-Mechanical Systems) and is made up of two separate calorimeters on a removable sensor chip (Fig. 2). It consists of two identical quadratic silicon nitride membranes with a length of 1.6 mm and a thickness of 2 μm. The sample area with a diameter of 0.5 mm is in the middle of the membrane and is coated with aluminium so that a homogeneous temperature profile is obtained. The temperature of this area is measured by means of eight thermocouples and resistive heaters are used to heat very quickly. Samples can be prepared and cycled many times to understand the effect of high heating and cooling rates, stored for archiving purposes and re-investigated again at a later date. Typical polymer samples for the Flash DSC 1 have a thickness of 10 to 50 μm and small disks are first cut from the bulk material. Organic materials typically have a mass between 10 ng and 10 μg and the mounted stereo microscope aids sample preparation and placement.
The Flash DSC 1 opens the door to the wider experimental parameters required to investigate the meta-stable and time-dependent transitions of materials. Very fast cooling and heating rates allow researchers to generate material under real process conditions (cooling) and then measure those material properties (heating) to gain a never before seen perspective into their materials.
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